(ST. LOUIS) -- A lawyer from Maryland struck a Des Peres police officer with her vehicle and then led authorities on a high-speed chase before being apprehended late Thursday night, police said.

Joelle Louise Williams, 38, of Silver Spring, Md., was caught when she swerved off Interstate 270 to avoid a police roadblock and was charged with second-degree assault of a police officer. She was held Friday on $ 20,000 bond at the St. Louis County Jail.

The Des Peres officer, Ed Scognamiglio, suffered a bruised left arm. Williams also damaged five vehicles in the chase, one of them a police car, authorities said. There were no other injuries.

Des Peres Police Chief William Bridges said he did not know why Williams fled. He said it did not appear that Williams was intoxicated or committed any crime beforehand. "Her excuse for running was that she was scared," Bridges said. "But we can't figure out what she was scared of."

Bridges said his officers responded to a report at 9:50 p.m. Thursday from residents on Roth Drive that a woman, later identified as Williams, was acting strangely in a parked 1999 Isuzu Rodeo without license plates.

Two officers approached Williams' car and noticed there were two dogs and a cat inside with her. "The car was also completely loaded with all kinds of papers and pet food and what I'd call junk," Bridges said.

When the officers tried to speak to Williams, she rolled up her window and sped off, striking Scognamiglio with her side mirror and knocking him to the ground, police reported. Scognamiglio got into his car and gave chase. Williams pulled over a short distance later, on Ballas Road. When Scognamiglio pulled his patrol car alongside hers, Williams rammed his vehicle and raced off again, according to police.

She got on Interstate 270 and drove at high speed, Bridges said. Creve Coeur police and the Missouri Highway Patrol joined in the pursuit. Authorities set up a roadblock on the highway in Bellefontaine Neighbors, near the exit to Highway 367. Williams swerved off the interstate and sideswiped four civilian vehicles on the shoulder before stopping, police said.

Bridges said police were justified in pursuing because Williams had struck an officer and didn't have license plates, which would have made it difficult to track her down. Police said Williams had been staying at a hotel in North County and told them she planned to settle here and start a law practice.